PPRuNe Forums - View Single Post - Turbo fan anomaly... driving me nuts and I don't have many left to lose
Old 5th Jul 2022, 20:16
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fdr
 
Join Date: Jun 2001
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Originally Posted by Private jet
The high ITT engine is degraded or damaged in some way. In order to generate as much thrust as the "good" engine, it is burning more fuel/requires more heat and it's not being usefully used, hence the higher than normal turbine temp. Compressor damage (lower pressure ratio= less thermal efficiency), leaky surge bleeds, degraded turbine (pressure/temp drop across the turbine is in ilne with power extraction and is a known quantity at the design stage).
quite true, in this case however there is no increase in fuel burn at all if N1s are matched with a variation in ITT. That is the oddity. Over 1000 tons of fuel burn there is no difference in fuel burns.

Sig229 I used to fly the Lear 45 with TFE-731s, it was long enough ago I don't recall many of the finer details. We did have engine sync, could couple to either N1 or N2. I don't recall ever being temp limited in that one engine was operating hotter enough than the other to the point it would affect operation. Same in the 737, the EEC does all the work determining thrust setting based on ambient conditions. The only time I've ever been limited by ITT was flying turboprops, we would set power by torque unless we hit maximum ITT then that would be max power for that current condition. If the engine "temped out" before reaching a minimum torque value there was something wrong and maintenance would have to look into it.
A number of power settings are specifically ITT, the LR45 has a heavily derated engine, the TFDE731-20AR which is around a 20% derate from the same configuration in the -40. For those engines, that's around a 50C difference in ITT margin.
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